The invention relates to an injection nozzle for use in controlling fluid flow through an outlet. In particular, but not exclusively, the invention relates to an injection nozzle for use in a fuel injector for delivering fuel to an internal combustion engine.
FIG. 1 shows an enlarged view of a conventional injection nozzle of a fuel injector comprising a valve needle 10 which is movable within a blind bore 12 provided in a nozzle body 14. A region of the valve needle 10, having a diameter 10a, is engageable with an annular valve seating 16 defined by a portion of the bore 12 to control fuel delivery through a set of outlet openings 18 provided in the nozzle body 14. In use, when the valve needle 10 is moved in an upward direction in the illustration shown away from the valve seating 16, fuel within a delivery chamber 19, defined by the bore 12 and the outer surface of the valve needle 10, is able to flow past the valve seating 16 and out through the outlet openings 18 into an associated engine cylinder or other combustion space.
The valve needle is provided with a compression spring (not shown) which serves to urge the valve needle against the valve seating 16 to prevent fuel injection through the outlet openings 18. Movement of the valve needle 10 away from the valve needle seating 16 to commence fuel injection may be controlled in several ways. For example, the pressure of fuel supplied to the delivery chamber 19 may be increased until such time as the force applied to the thrust surfaces (not shown) of the valve needle 10 is sufficient to overcome the spring force, thereby causing the valve needle 10 to be urged away from the valve seating 16 to permit fuel delivery through the outlet openings 18.
It is an important feature of fuel injector design that the fuel pressure at which the valve needle 10 moves away from the valve seating 16 to cause fuel injection to be commenced can be achieved with high accuracy. In order to achieve this, the effective diameter of the annular valve seating 16 against which the valve needle 10 seats must be machined and finished with high accuracy. During manufacture, it is therefore important to minimize variations in the effective diameter and in the surface finish of the valve seating 16. However, in practice, a high level of repeatability in the effective diameter and surface finish of the valve seating is difficult to achieve.
It is an object of the present invention to alleviate this problem.
According to a first aspect of the present invention, there is provided an injection nozzle for delivering fuel to a combustion space, the injection nozzle comprising a valve member including a first region of substantially frusto-conical form defining a seating surface which is engageable with a valve seating surface to control fuel delivery from the injector, and a second region arranged such that, when the valve member is seated against the valve seating surface, in use, the second region is located downstream of the valve seating surface, wherein the first region subtends a first cone angle which is greater than a second cone angle subtended by the second region.
The injection nozzle may preferably comprise a nozzle body provided with a blind bore within which the valve member is slidable, the blind bore defining the valve seating surface for the valve member. The nozzle body is preferably provided with at least one outlet opening through which fuel is delivered when the valve member is lifted from the valve seating surface.
The valve member is slidable within the blind bore, in use, to move the valve member in and out of engagement with the valve seating surface.
The invention permits the effective diameter of the valve seating to be achieved with greater accuracy and with greater repeatability during manufacture. As the second region of the valve member subtends a smaller cone angle than the first region, neither the portion of the first region downstream of the seating surface nor the second region can seat against the bore. Thus, the effective diameter of the surface of the valve member which seats against the valve seating, and hence the effective diameter of the valve seating, can be more accurately defined. High accuracy machining and finishing of valve seating is therefore less critical.
The invention also provides the advantage that high accuracy machining of the outer surface of the valve member is easier to achieve than high accuracy machining of the inner surface of a blind bore.
Preferably, the angular difference between the first cone angle subtended by the first region and the second cone angle subtended by the second region is substantially 1o.
Preferably, the first cone angle subtended by the first region may be substantially 61xc2x0 and the second cone angle subtended by the second region may be substantially 60xc2x0.
Preferably, the length of the first region along the axis of the valve member may be less than or equal to 0.2 mm. The diameter of the first region, at the point at which the seating surface engages the valve seating surface, may be, for example, substantially 2.25 mm.
Conveniently, the second region of the valve member may be an end region of the valve member. The end region of the valve member may be of substantially frusto-conical or conical form.
The injection nozzle is suitable for use, for example, in unit/pump injectors and in fuel injectors arranged to be supplied with fuel from a common rail.
According to a second aspect of the present invention, there is provided a valve member for use in a filet injector or injection nozzle as herein described for delivering filet to a combustion space, the valve member comprising a first region of substantially frusto-conical form defining a seating surface which is engageable with a valve seating surface to control fuel delivery from the injector, and a second region arranged such that, when the valve member is seated against the valve seating surface, in use, the second region is located downstream of the valve seating surface, wherein the first region subtends a first cone angle which is greater than a second cone angle subtended by the second region.
The differential angle between the valve seating surface and the seating surface defined by the first region is preferably at least 1.5xc2x0.
According to a further aspect of the present invention, there is provided a method of manufacturing an injection nozzle for use in delivering fuel to a combustion space, the injection nozzle comprising a nozzle body and a valve member, the method comprising;
providing the nozzle body with a blind bore which is shaped to define a valve seating surface,
machining the valve member to include a first region of substantially frusto-conical form which is shaped to subtend a first cone angle, the first region defining a seating surface which is engageable with the valve seating surface to control fuel delivery from the injection nozzle, and
machining the valve member to include a second region which, when the valve member is seated against the valve seating surface, in use, adopts a position in which it is located downstream of the valve seating surface, and is shaped to subtend a second cone angle, wherein the first and second regions of the valve member are machined such that the first cone angle is greater than the second cone angle.
The method of manufacture permits the effective diameter of the valve seating to be achieved with greater accuracy and with greater repeatability during manufacture. Using this method, high accuracy machining and finishing of valve seating is less critical, as described previously.